The invention relates generally to electronic printed circuit boards, and more specifically to high-density jumper connection via a ball grid array.
Electronic components are typically assembled into complex circuits by mounting them on printed circuit boards. These printed circuit boards are usually flat nonconductive boards with one or more layers of a conductive material such as copper fixed on or in the printed circuit board. The layers of copper are etched or otherwise formed to specific shapes and patterns in the manufacturing process, such that the remaining conductive copper traces are routed to connect electrical components to be attached to the printed circuit board.
It is not uncommon for printed circuit boards such as these to have copper layers on both a top and bottom side of the circuit board, but also several layers of copper traces or patterns sandwiched at various depths within the circuit board itself. These traces allow greater flexibility in circuit routing, and usually allow designing a more compact circuit board for a particular circuit than would otherwise be possible. The various layers are sometimes dedicated to particular purposes, such as a ground layer that only serves to distribute ground or signal return connections to various components.
Multiple layers that serve to connect components to other components often must be connected to components attached to a different layer (top or bottom) or the layers must be attached to each other at selected points, requiring use of what are commonly known as vias. These vias typically are essentially small conductive plated-through hole elements oriented perpendicular to the top and bottom surfaces of a circuit board that extend through at least two conductive layers of the circuit board, and that electrically connect circuit traces on at least two of the conductive layers to each other.
But, each layer of a printed circuit board adds a significant amount of cost to the board, making use of as few layers as are practical to achieve the desired performance and configuration economically desirable. For example, it is estimated that for a printed circuit board of standard ATX personal computer motherboard size, the difference in board cost alone between a four-layer printed circuit board and a six-layer circuit board is approximately seven dollars. Unfortunately, the increasingly dense components used in modem electronic systems and the relatively complex power requirements of such systems can make designing a four-layer circuit board virtually impossible. As an example, a modem personal computer has hundreds of connections between the processor, chipset, memory, and attached bus, in addition to the required power distribution that may include 12 v, 5 v, 3.3 v, and other voltages at increasingly high current levels as transistor counts and clock speeds continue to increase.
The dilemma that is then faced by motherboard designers is how to create a densely routed motherboard that is cost-effective and has as few layers as is practical to achieve. What is desired is a way of enabling printed circuit board designers to design circuit boards with as few layers as is practical while enabling the high routing densities that sometimes require a greater number of circuit board layers.